MOLTEN Al-Zn-BASED PLATED SHEET STEEL, SURFACE-TREATED STEEL PLATE, COATED STEEL PLATE, AND METHOD FOR MANUFACTURING MOLTEN Al-Zn-BASED PLATED SHEET STEEL

Abstract

To provide a molten Al-Zn-based plated sheet steel with excellent plating adhesiveness at a bending-back part even when a plating adhesion amount is large.SOLUTION: The present invention relates to a molten Al-Zn-based plated sheet steel, on which a plating layer having a composition containing 40-70 mass% of Al and 0.5-3.0 mass% of Si, and Zn and inevitable impurities at a remainder, is formed. The plating layer has a dendrite gap mainly containing dendrite made of Al primary crystal and Al-Zn eutectic crystal. The thickness X (μm) of the plating layer and the Vickers hardness HV0.01 of the Al primary crystal satisfy the following expressions (1) and (2). HV0.01≤-4X+205...(1) X≥23...(2)SELECTED DRAWING: Figure 4

Claims

1. A hot-dip Al-Zn plated steel sheet having a plating layer formed thereon, the plating layer having a composition containing 40 to 70 mass% Al, 0.5 to 3.0 mass% Si, and the balance being Zn and unavoidable impurities, The plating layer has dendrites mainly composed of Al primary crystals and dendritic gaps containing Al-Zn eutectic, The thickness X (μm) of the plating layer and the Vickers hardness HV ０．０１ and (2) satisfy the following relationships (1) and (2): HV ０．０１ ≦-4X+205 ・・・(1) X≧23 ... (2)

2. The hot-dip Al-Zn coated steel sheet according to claim 1, characterized in that in a bending test in accordance with JIS G 3322 (2019), a 180-degree close bending is performed with a width of 125 mm without placing a plate in the inner space of the bend, the close bending portion is returned to be smooth, and then an adhesive tape is applied to the surface of the returned portion that was on the inside during the close bending, and the tape is peeled off in a direction perpendicular to the bend line of the returned portion, and the maximum width of the peeled plating layer adhering to the adhesive tape in the direction perpendicular to the bend line is 1 mm or less.

3. A surface-treated steel sheet, comprising the hot-dip Al-Zn plated steel sheet according to claim 1 or 2, and a chemical conversion coating formed on the hot-dip Al-Zn plated steel sheet.

4. A coated steel sheet comprising the hot-dip Al-Zn plated steel sheet according to claim 1 or 2, and a coating film formed directly or via an intermediate layer on the hot-dip Al-Zn plated steel sheet.

5. forming a plating layer having a plating thickness of X (μm) per side on a base steel sheet using a plating bath having a composition containing 40 to 70 mass% Al, 0.5 to 3.0 mass% Si, and the balance being Zn and unavoidable impurities; and reheating the steel sheet on which the plating layer is formed. a manufacturing method of a hot-dip Al-Zn coated steel sheet, characterized in that, when a maximum temperature reached by the steel sheet during the reheating is T°C and a cooling time from T°C to 100°C is y (hr), the following relationships (2), (3), and (4) are satisfied: X≧23 ... (2) 150≦T≦300 ... (3) 0.5≦y≦24 ... (4)

Images